diff --git a/tests/extmod/ujson_dump_separators.py b/tests/extmod/ujson_dump_separators.py
new file mode 100644
index 0000000000..e19b99a26d
--- /dev/null
+++ b/tests/extmod/ujson_dump_separators.py
@@ -0,0 +1,62 @@
+try:
+    from uio import StringIO
+    import ujson as json
+except:
+    try:
+        from io import StringIO
+        import json
+    except ImportError:
+        print("SKIP")
+        raise SystemExit
+
+for sep in [
+    None,
+    (", ", ": "),
+    (",", ": "),
+    (",", ":"),
+    [", ", ": "],
+    [",", ": "],
+    [",", ":"],
+]:
+    s = StringIO()
+    json.dump(False, s, separators=sep)
+    print(s.getvalue())
+
+    s = StringIO()
+    json.dump({"a": (2, [3, None])}, s, separators=sep)
+    print(s.getvalue())
+
+    # dump to a small-int not allowed
+    try:
+        json.dump(123, 1, separators=sep)
+    except (AttributeError, OSError):  # CPython and uPy have different errors
+        print("Exception")
+
+    # dump to an object not allowed
+    try:
+        json.dump(123, {}, separators=sep)
+    except (AttributeError, OSError):  # CPython and uPy have different errors
+        print("Exception")
+
+
+try:
+    s = StringIO()
+    json.dump(False, s, separators={"a": 1})
+except (TypeError, ValueError):  # CPython and uPy have different errors
+    print("Exception")
+
+# invalid separator types
+for sep in [1, object()]:
+    try:
+        s = StringIO()
+        json.dump(False, s, separators=sep)
+    except TypeError:
+        print("Exception")
+
+# too many/ not enough separators
+for sep in [(), (",", ":", "?"), (",",), []]:
+    try:
+        s = StringIO()
+        json.dump(False, s, separators=sep)
+    except ValueError:
+        print("Exception")
diff --git a/tests/extmod/ujson_dumps_separators.py b/tests/extmod/ujson_dumps_separators.py
new file mode 100644
index 0000000000..efb541fe8b
--- /dev/null
+++ b/tests/extmod/ujson_dumps_separators.py
@@ -0,0 +1,60 @@
+try:
+    import ujson as json
+except ImportError:
+    try:
+        import json
+    except ImportError:
+        print("SKIP")
+        raise SystemExit
+
+for sep in [
+    None,
+    (", ", ": "),
+    (",", ": "),
+    (",", ":"),
+    [", ", ": "],
+    [",", ": "],
+    [",", ":"],
+]:
+    print(json.dumps(False, separators=sep))
+    print(json.dumps(True, separators=sep))
+    print(json.dumps(None, separators=sep))
+    print(json.dumps(1, separators=sep))
+    print(json.dumps("abc", separators=sep))
+    print(json.dumps("\x00\x01\x7e", separators=sep))
+    print(json.dumps([], separators=sep))
+    print(json.dumps([1], separators=sep))
+    print(json.dumps([1, 2], separators=sep))
+    print(json.dumps([1, True], separators=sep))
+    print(json.dumps((), separators=sep))
+    print(json.dumps((1,), separators=sep))
+    print(json.dumps((1, 2), separators=sep))
+    print(json.dumps((1, (2, 3)), separators=sep))
+    print(json.dumps({}, separators=sep))
+    print(json.dumps({"a": 1}, separators=sep))
+    print(json.dumps({"a": (2, [3, None])}, separators=sep))
+    print(json.dumps('"quoted"', separators=sep))
+    print(json.dumps("space\n\r\tspace", separators=sep))
+    print(json.dumps({None: -1}, separators=sep))
+    print(json.dumps({False: 0}, separators=sep))
+    print(json.dumps({True: 1}, separators=sep))
+    print(json.dumps({1: 2}, separators=sep))
+
+try:
+    json.dumps(False, separators={"a": 1})
+except (TypeError, ValueError):  # CPython and uPy have different errors
+    print("Exception")
+
+# invalid separator types
+for sep in [1, object()]:
+    try:
+        json.dumps(False, separators=sep)
+    except TypeError:
+        print("Exception")
+
+# too many/ not enough separators
+for sep in [(), (",", ":", "?"), (",",), []]:
+    try:
+        json.dumps(False, separators=sep)
+    except ValueError:
+        print("Exception")